Structural factors directing nanosized polyion complex vesicles (Nano-PICsomes) to form a pair of block aniomer/homo catiomers: Studies on the aniomer segment length and the catiomer side-chain structure

Much attention has been devoted to precise control of the size and morphology in nanosized molecular assemblies for a wide range of materials applications. Recently, we reported observing submicron/nanosized polyion complex vesicles (Nano-PICsomes) with a narrow size distribution, synthesized using specific types of homocatiomers and polyethylene glycol (PEG)-based block aniomers. However, only one example of Nano-PICsomes has been reported to date. Here, the role of the chemical composition of PEG-based block aniomers and the chemical structures of the side chains of homocatiomers were carefully examined to better understand the formation of Nano-PICsomes. Transmission electron microscopy and dynamic light scattering analyses of Nano-PICsomes revealed that a longer length of ionic segments in the block aniomers or a PEG weight fraction (f PEG) <10%, is required for the selective formation of Nano-PICsomes, whereas polymer combinations with f PEG >10% produced spherical micelles. In addition, the homocatiomers containing longer aliphatic side chains (e.g., five or six carbon atoms) favored the formation of Nano-PICsomes, whereas those containing shorter aliphatic side chains produced irregularly shaped PIC micelles. Accordingly, f PEG and the length of the side chain were found to be the key factors that control the morphologies of Nano-PICsomes. Insights gained from this study can broaden the spectrum of the design of Nano-PICsomes for use in a diverse range of material applications.